1. Field of the Invention
This invention relates to a tape cassette used as a recording medium for a video tape recorder, for example, and more particularly, to a lock lever adapted for locking a lid mounted rotatably to the front side of the cassette in the closed state.
2. Description of the Prior Art
In a conventional tape cassette used as the recording medium for a recording and/or reproducing apparatus, such as a video tape recorder, a front cover or lid is rotatably mounted to cover the front side of a cassette in which a pair of tape reels about the outer periphery of which a tape is wound is rotatably supported and accommodated. This lid covers the front side of the cassette to protect the tape extending on this front side. The lid has an attachment piece provided with an engaging aperture and is adapted to be locked in the closed state by a locking lever that is provided in the tape cassette and that engages in the engaging aperture in the closed state of the lid.
As shown in FIG. 1, the lock mechanism for locking the lid in the closed state includes the aforementioned lock lever 103 rotatably supported by a supporting shaft 102 projectingly mounted from a base plate at the front side corner of the lower cassette half 101 and a torsion coil spring 104 adapted for biasing the lock lever 103 so as to be turned towards the outer side of the lower half 101. The lock lever 103 of the lock mechanism has a lateral engaging portion 105 projectingly mounted to one lateral side of the foremost part thereof and an upright engaging portion 107 at the mid part thereof engaged by one end 106 of the torsion coil spring 104. The torsion coil spring 104 has its coil portion 108 engaged with the foremost part of a supporting shaft 109 projectingly mounted adjacent to the supporting shaft 102. The one end 106 of the coil spring 104 is engaged with the upright engaging portion 107 so that the lock lever 103 is urged to be turned in a direction in which the lateral engaging portion 105 is inserted into and engaged with a lock lever aperture 110 bored in the side wall of the lower cassette half 101 so as to be projected out of the lower cassette half 101. The arrangement is so made that the portion of the lateral engaging portion 105 projecting out of the lower cassette half 101 is inserted into and engaged with an engaging aperture formed in the attachment member of the lid when the latter is in the closed state.
When the tape cassette is mounted to the recording and/or reproducing apparatus, a release pin 50 provided to the recording and/or reproducing apparatus is intruded into the cassette 112 through a release opening 111 formed in the lower cassette half 101 adjacent to the lock lever aperture 110 to thrust an abutment portion 113 formed on the surface at the mid portion of the lock lever 103 facing to the lateral wall of the lower cassette half 101 to turn the lock lever 103 inwardly of the tape cassette 112 against the biasing force of the torsion coil spring 104 for receding the lateral engaging portion 105 into the inside of the tape cassette 112. As a result thereof, the engagement between the engaging portion 105 and an engaging aperture 115 in the lid 114 is released to permit rotation of the lid 114. The latter is caused to be turned and opened by a lid opening and closing device provided to the recording and/or reproducing apparatus so that the tape extending on the front side of the tape cassette is exposed.
In the above state, it becomes possible to draw out the tape 116 from the front side of the cassette towards the recording and/or reproducing apparatus by the operation of the apparatus to permit the operation of the recording and/or reproduction.
Heretofore, owing to the mounting tolerance of the lock lever 103 and the molding error of the tape cassette 112, the abutment position of the release pin 50 on the lock lever 103 occasionally was not constant. That is, the distance between the release pin 50 and the supporting shaft 102 in a direction orthogonal to the direction of movement of the release pin 50 or the direction shown by the arrow mar A indicated in FIG. 2, that is, the distance x in FIG. 2, will differ from cassette to cassette, such that, when the release pin 50 has completed the unlocking or release operation, that is, when the release pin 50 has completed the movement over the predetermined distance or stroke, the lock lever 103 may have been turned a widely variable angle. When the distance between the release pin 50 and the supporting shaft 102 at the time of completion of the above described release operation becomes shorter than a predetermined value, the lock lever 103 may have been turned a distance larger than a predetermined distance, such that, as shown in FIG. 2, the foremost part of the lock lever 103 facing to the tape 116 may be contacted with the tape 116. When the tape reel is caused to be turned in this state to cause the running of the tape 116, the later undergoes friction at the contact portion with the lock lever 103. In such case, the stable running of the tape may be obstructed or the tape may be damaged at the contact portion resulting in the deterioration of the recording and reproducing characteristics of the tape 116 or worsening its recording and record keeping properties.